I have a Samsung SIR-T451. As with all of you, the basic rabbit ears that worked great for analog does not for digital. I have pixelation, sound loss, etc with some channels. For me, VHF channels are hard for me to pull in because the rabbit ears I have are an open dipole like you see on many rooftop antennas, with the proper size for UHF, not VHF. An FCC search comes up with my local ABC, CBS ,NBC, FOX, CW, and PAX (Ion TV now) all transmit at around 10% of the analog ERP, My local PBS transmits at around 20%(big deal) of it's analog ERP. To me, this explains everything. Signal levels are so low that error correction can't really handle it. I had to use a VHF/UHF/FM/cable distribution amplifier to bring it up to a level that most stations don't pixelate. Analog reception is good enough and watchable, and actually pretty decent. Unless they turn up the power, digital reception will really be problematic. I remember reading on this thread about the FCC not doing proper testing/not being ready for the switchover. Just look at the crap called "HD Radio" they approved. Closed standard, one company's closed and monopolized standard, expensive equipment. The FCC really needs to get their heads out of their a$$.
For connecting ATSC tuners to your vintage TVs, just connect the box to a Rat Shack modulator (if you use B/W sets, connect the luma instead of composite video) and you should be good to go. Most of you guys still use the rotary tuners on your old sets, but all the vintage sets I have all have VHF tuners only, and there are no analog VHF stations in my area, so my tuners are always tuned to channel 3.
As for those with cable, I'd highly recommend getting rid of it. We have c***ast in my area and they are nothing but money hungry bastards that provide crappy service. I'd recommend satellite if you can. Satellite reception is closer to the roots of TV reception. To go even better, go c-band. If you have the permission/land/etc, put up a c-band dish, infact put up more than one if you can. Go to a c-band provider and subscribe to direct feeds of your favorite channels. Better picture because they are not compressed by transmission through DBS/cable, better rates, and in my opinion, just a better way to watch TV. Also, don't forget the free channels like Deutsche Welle TV (my favorite) and other in the clear channels on c band and ku band.
If you really want the ultimate solution, and can get equipment used, put up a c-band dish for every bird you want to get reception from (Say AMC 11 for Discovery networks), connect it to Digicipher II and DVB satellite receivers with ASI outputs (an output of the direct transport stream) and connect those outputs to ASI input PCI cards in a mythtv backend system. Each ASI input is a channel, and some cards have multiple inputs and some receivers can have multiple ASI outputs. This is how headends pull in the channels, but you can do it yourself and run a kick ass IPTV system with mythtv. Granted, this is expensive, complicated, can require lots of power, and there is lots of stuff that can go wrong or just not work at all. But, if you can get the equipment c-band subscriptions, the space for the dishes, and the ASI input PCI cards and get them playing nice with mythtv, you will be in your glory. You won't ever have to upgrade anything for at least 15 or 20 years, either. This is just one of my dreams.
Oh, one thing I forgot to mention. Some vintage TVs (like the Philco Safari) have no external antenna input. The solution for that is to use a small transmitter. Or, if you are brave, remove the antenna, and in the hole it left in the case, put an F connector there. Some situations this might not work well.
Jonathan